Each year, floods are a major cause of economic loss and loss of life in the United States, causing millions of dollars in damages each year. In addition, floods cause much inconvenience to those affected by the flood due to cleanup, temporary or permanent relocation, etc. It should be possible to mitigate economic loss, inconvenience, and loss of life by more accurately predicting and conveying information regarding specific geographic areas that will be affected by flooding.
Flood warnings provided by the National Weather Service (NWS) are presently not user-friendly. For example, an actual flood warning issued by the NWS for Wilmington, N.C. on Nov. 20, 2002 is shown in FIG. 1. The flood warning includes river stage levels at which a flood will or is predicted to occur. A river stage level refers to the river's depth at a certain location relative to an arbitrary level on a flood gauge. Because most flood gauge levels are arbitrary, they can be confusing to the general public and even to emergency responders such as fire and police. For example, it is possible to have a negative (i.e., below zero) river level, even though there is water in the channel. These arbitrary readings cause a great deal of confusion and can even be dangerous, as described in Who Decides? Forecasts and Responsibilities in 1997 Red River Flood, by Roger A. Pielke, Jr., Applied Behavior Science Review, 1999, 7(2), 83-101).
In addition, very few members of the general public know whether they will be affected by a flood based on the textual warning illustrated in FIG. 1 because very few people, if any, are aware of the height of the their location in terms of river stage levels in relation to a specific river gauge. River gauge information, for the public, only becomes important when there is an imminent threat, by which time it is typically too late to mount an educational program. Likewise, emergency officials (e.g., police and fire) are also often unaware of potential flood areas, and cannot accurately prepare for potential flooding or emergency response. Thus, someone familiar with interpreting NWS warnings must translate each warning into a form understandable to the general public in order to provide any sort of understandable flood warning. While newscasters (e.g., via television) often attempt to provide flood warnings, they are generally limited to a broad verbal indication that flooding is possible, and to take necessary precautions. At best, they convey these same technical river level forecasts.
One known means of providing improved flood warnings is through the use of inundation maps. An inundation map is a geographical map indicating areas likely to be flooded as a result of receiving an inundation of water, e.g., from rain, a dam bursting, tsunami, hurricane, or the like. However, most inundation maps created to date are used for estimating the theoretical effects of major natural disasters, not for predicting possible flood areas as a result of rain, and are not prepared in real-time. For example, inundation maps have been used to predict water levels as a result of global warming (e.g., as the icecaps melt), storm surge due to a hurricane, tsunami, a dam bursting, and the like. These inundation maps are created using complex models not based on rainfall prediction or flood warnings from the NWS or some other meteorological prediction service.
The NWS is presently working on developing an advanced hydrologic prediction service (AHPS) to determine a probability that a specific area will flood within a 60-day period. For each specific area, the AHPS indicates one of four probability ranges: >75%, 50-75%, 25-50%, and <25%. The AHPS inundation map is derived from NWS long-term, hydrologic Ensemble Streamflow Prediction (ESP) products. The inundation map gives no information about flood depth above the ground, river stage, flood frequency, or flood return interval nor does the AHPS provide real-time flood information based on imnminent weather. Thus, the AHPS inundation maps are unsuitable for providing flood warnings to the general public based on short-term events, such as a heavy rainstorm.
There are private sector consulting firms which create mesoscale models for small river basins which are capable of generating river stage heights which can be, and in some cases are, turned into inundation maps. However, these are used exclusively on small streams and basins. They do not output contingency levels nor do they produce animated inundation maps suitable for broadcast use.
As indicated above, a river's stage level refers to the depth of the river at a specific location. However, the stage level is indicated and referred to in terms of water depth at that single location only, and is not represented as a uniform measurement throughout a river across multiple river gauges, or between rivers (e.g., where one river feeds into another river). A river gauge is a common tool used to indicate the stage of a river at the location of the river gauge. River gauges, generally, are known in the art and are discussed in detail in U.S. Geological Survey Circular 1123, Stream-Gaging Program of the U.S. Geological Survey, 1995. However, because river gauges are not calibrated to a uniform or normalized depth measurement (similar to time being able to be described in Greenwich mean time, or Zulu time), data cannot be consistently plotted for an entire river, or across rivers, using data from multiple river gauges.
For example, with reference to FIG. 2, suppose a river 201 has two river gauges 203 and 205, and that the flood stage of the river at each gauge is ten feet. That is, if the river's stage reaches ten feet at either gauge, then the river will overflow its banks and begin to flood. Assume as well that the river 201 flows to the east. Thus, a river stage of ten feet at gauge 203 will necessarily be higher in elevation than a river stage of ten feet at gauge 205, because the river must necessarily flow downhill. This elevation discrepancy creates a problem when attempting to calculate and illustrate on the geographic map the stage level of the river that is required in order for location 207 to be flooded. That is, location 207 can be said to flood at river stage X according to gauge 203, or at river stage Y according to gauge 205, providing inherent confusion when attempting to merge information from two or more river gauges. Flood information thus cannot be plotted accurately for large areas of land using localized river stage information from multiple river gauges.
It would be an advancement in the art to create an improved method of forecasting floods in real time with specificity. It would be a further advancement in the art to provide a way to normalize river gauge measurements so that localized data from multiple river gauges could be used together. It would be a further advancement in the art to develop an improved warning system such as an inundation map to provide clear, understandable flood warnings to members of the general public that also includes the inevitable uncertainty in forecast river stages as a real time heavy rain and flooding event unfolds